Hot Stainless Steel Surface Research Articles

Analysis of Reaction Products After Ignition Process of 1-octanol/air Mixtures on a Hot Surface

1-octanol is considered an alternative to conventional diesel. In order to know the ignition parameters of 1-octanol, an experimental study of the explosive combustion of 1-octanol/air mixtures at ambient pressure and various initial temperatures was performed on a hot stainless-steel surface in a closed vessel. The ignition temperatures of 1-octanol/air mixtures at different initial conditions were determined. Using gas chromatography-mass spectrometry (GC-MS) and gas chromatography with flame ionisation detector (GC-FID) methods, the composition of the reaction products was investigated.

Study on the effect of Weber Number to heat transfer of multiple droplets on hot stainless steel surface

Multiple droplets are drops of water that continuously dropped onto a surface. Spray cooling is an application of the use of droplet on a cooling system. Spray cooling is usually used in a cooling system of electronic devices, and material quenching. In this study, correlations between Weber number and surface temperature decrease rate during multiple droplets impingement are investigated and analyzed. Visualization process is used to help determine the evaporation time of droplets impingement by using high speed camera. Induction stove is used to maintain a stainless steel surface temperature at 120°C, 140°C, and 160°C. The Weber number was varied at 15, and 52.5 to simulate low and medium Weber number. The result of this study shows that increase in Weber number does not increase the temperature decrease rate noticeably. Whereas the Weber number decrease the time required for surface temperature to reach its lowest surface temperature. It was also found that for low and medium Weber number, Weber number affect the evaporation time of multiple droplets after impingement.

Rewetting and maximum surface heat flux during quenching of hot surface by round water jet impingement

The transient cooling of hot stainless steel surface of 0.25mm thickness is done with round water jet impingement. Initially, the surface was heated up to the temperature of 800°C before the water was injected through straight tube type nozzle of 2.5mm diameter and 250mm length. During impingement cooling, the surface temperature was measured up to 12mm radial distance away from the stagnation point. The jet exit to surface spacing, z/d, and jet Reynolds number, Re, varied in the range of 4–16 and 5000–24,000 respectively. The surface rewetting and transient heat flux of the test-surface was studied for these operating parameters.During impingement cooling process the initial rewetting occurred at stagnation region with the lowest wetting delay period. In fact, the rewetting temperature, rewetting velocity and the maximum heat flux reduced for extreme spatial location. However, the wetting delay increased significantly for the locations away from the stagnation point. The surface rewetting and transient heat flux were increased with the rise in jet Reynolds number, resulting in the enhancement in rewetting temperature, rewetting velocity and reduced wetting delay. The maximum heat flux was obtained for 4–6mm radial location. The effect of jet exit to surface spacing on the rewetting parameters is found to be marginal. A correlation has been developed which predicted the maximum heat flux within an error band of ±10%.

Characterization and Improvement of Signal Drift Associated with Electron Ionization Quadrupole Mass Spectrometry

Quadrupole mass spectrometry with electron ionization (EI-QMS) is a very popular detection technique in combination with gas chromatography. It is deployed for the analysis of volatile and semivolatile analytes in many industry domains. Although a very important factor for quantitative analysis, little is known about the stability of ion source performance. Only a few papers and patents report possible signal instabilities due to sample adsorption, degradation, or insulating deposits on the hot stainless steel surface of the ion source. In this study, a conventional stainless steel ion source was used to investigate possible signal drifts. It was observed that the EI-QMS instrument indeed suffered from continuous signal instability. It was found that the key parts which are responsible for the signal instabilities are those that regulate the ion beam toward the mass analyzer: the repeller, exit plate, and focusing lenses. The voltage of the repeller was found to have a major influence on the signal stability. The surface of the repeller, exit plate, and focusing lenses was modified by applying a gold coating. It was demonstrated that the signal stability of the MS dramatically improved when using the gold-coated parts. The contribution of each part to the stability improvement was quantitatively determined and compared with the standard stainless steel source performance. It was assumed that the signal drift observed with the stainless steel EI source originated from charge buildup on the surfaces. This hypothesis was supported by software simulations.

On the collision behaviors of a diesel drop impinging on a hot surface

The collision of diesel oil drops ranging from 500 μm to 950 μm on an inclined hot stainless steel surface was experimentally observed for the purpose of discovering the contrast between the collision behaviors of diesel drops and those of other liquids. The experimental results may improve the understanding of fuel drops impact characteristics. Results showed that the critical Weber number for disintegration was very different from the criteria presented by previous researchers for other liquids. The resident time on the hot surface was found to be independent of the impinging angle and normal impinging velocity, and about 30% higher than the free oscillation prediction. An empirical correlation of non-dimensional resident time was built up as a function of the normal Weber number alone. Also, an approximation based on a simple energy balance was presented for the maximum spreading diameter. These two approximations were in a good agreement with the experimental data.

CHARACTERISTICS OF WATER DROPLET IMPACTION BEHAVIOR ON A POLISHED STEEL HEATED SURFACE: PART I

This paper, which is in two parts, presents the results and analysis of droplet impaction on a hot stainless steel surface. Part I of this study reports the results of analysis of high-speed visualizations of droplet impaction phenomena on a hot stainless steel surface, including the characteristics of reatomized droplets that are produced at high impact Weber numbers. The investigation extends to ranges of smaller droplets and higher velocities compared with published research. Part II will then provide the results and analysis of the droplet impaction heat transfer on a hot surface. The 3.0 mm diameter flat stainless steel surface was heated to temperatures of 140°C < Tw < 400°C, and water sprays were produced from a droplet generation system based on an 80 mm diameter rotary cup. Droplet sizes in the range 20 µm < D < 160 µm were used, impacting with velocities of 5 ms-1 < U < 18 ms-1 . Previous research relevant to the topic is reviewed. Physical models for different forms of droplet breakup in different regimes are developed from the new experiments and compared with existing models. Data are presented for the droplet spreading characteristics, as well as reatomized droplet characteristics, under relatively high impact Weber number conditions (i.e., 100 < We < 750), and for different boiling regimes. These data are correlated well using equations that can be justified by physical arguments.

CHARACTERISTICS OF WATER DROPLET IMPACTION BEHAVIOR ON A POLISHED STEEL HEATED SURFACE: Part II

This article presents the results and analysis of the droplet impaction on a hot stainless steel surface which is in two parts. Part I of this study reported the results of analysis of high speed visualisations of droplet impaction phenomena on a stainless steel hot surface, including the characteristics of reatomized droplets that are produced at high impact Weber number. Part II, herewith, provides the results and analysis of the droplet impaction heat transfer on a hot surface. The 3.0 mm diam flat stainless steel surface was heated to temperatures of 140°C < Tw < 400°C, and water sprays were produced from a droplet generation system based on an 80 mm diam rotary cup. Droplet sizes in the range 20 µm < D < 160 µm were used, impacting with velocities 5 ms-1 < U < 18 ms-1 . Previous research relevant to the topic is reviewed. The main purpose of this investigation was to independently analyse the effects of hydrodynamic parameters, such as droplet size, velocity, frequency, or mass flux, at different surface temperature conditions. The heat transfer results are presented and discussed in terms of overall heat flux results, although the contribution of the natural convection and radiative heat transfer (i.e., at the "no spray" condition) is also presented separately for better understanding of the results. The heat transfer effectiveness is also discussed and presented, indicating the cooling efficiency of the impacting sprays. Heat transfer effectiveness, ef, is found to decrease with increase in mass flux, which is similar in trend to that reported by other researchers. For a given mass flux, the maximum values of ef occur at Weber number 300 < We < 500 (39-62%). For a given mass flux and Weber number, the effect of increasing droplet size is to decrease ef.

Boiling during high-velocity impact of water droplets on a hot stainless steel surface

High-velocity impact of water droplets (0.55 mm diameter) on a heated stainless steel surface was photographed. To achieve high impact velocities, the test surface was mounted on the rim of a rotating flywheel, giving linear velocities of up to 50 m s −1 . Two cartridge heaters were inserted in the substrate and used to vary substrate temperature. A charge coupled device (CCD) video camera was used to photograph droplets impinging on the substrate. To photograph different stages of droplet impact, the ejection of a single droplet was synchronized with the position of the rotating flywheel and triggering of the camera. Substrate temperature was varied from 100 to 240 °C and the impact velocity from 10 to 30 m s −1 . High-resolution photographs were taken of vapour bubbles nucleating sites inside the thin liquid films produced by spreading droplets. An analytical expression was derived for the amount of superheat required for vapour bubble nucleation as a function of the impact velocity. For a given surface roughness, the amount of superheat needed decreased with impact velocity, which agreed with experimental results. For a fixed impact velocity, the maximum extent of droplet spread increased with substrate temperature.

The Effect of Dissolving Salts in Water Sprays Used for Quenching a Hot Surface: Part 1—Boiling of Single Droplets

We conducted experiments on the effect of dissolving three different salts sodium chloride (NaCl), sodium sulfate Na2SO4 and magnesium sulfate MgSO4 in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 90°C to 220°C. We photographed droplets as they evaporated, and recorded their evaporation time. At surface temperatures that were too low to initiate nucleate boiling all three salts were found to reduce droplet evaporation rates because they lower the vapor pressure of water. In the nucleate boiling regime, low concentrations (&lt;0.1 mol/l) of Na2SO4 and MgSO4 enhanced heat transfer because they prevented coalescence of vapor bubbles and produced foaming in the droplet, significantly reducing droplet lifetimes. Increasing the salt concentration further did not produce a corresponding increase in droplet boiling rate. Dissolved salts prevent bubble coalescence because they increase surface tension and stabilize the liquid film separating bubbles, and because electric charge that accumulates on the surfaces of bubbles produces a repulsive force, preventing them from approaching each other. Na2SO4 and MgSO4, which have high ionic strengths, produced a large amount of foaming in droplets and increased their boiling rate significantly. NaCl, which has low ionic strength, had little effect on droplet boiling.

Cooling effectiveness of a water drop impinging on a hot surface

We studied, using both experiments and a numerical model, the impact of water droplets on a hot stainless steel surface. Initial substrate temperatures were varied from 50°C to 120°C (low enough to prevent boiling in the drop) and impact velocities from 0.5 to 4 m/s. Fluid mechanics and heat transfer during droplet impact were modelled using a “Volume-of-Fluid” (VOF) code. Numerical calculations of droplet shape and substrate temperature during impact agreed well with experimental results. Both simulations and experiments show that increasing impact velocity enhances heat flux from the substrate by only a small amount. The principal effect of raising droplet velocity is that it makes the droplet spread more during impact, increasing the wetted area across which heat transfer takes place. We also developed a simple model of heat transfer into the droplet by one-dimensional conduction across a thin boundary layer which gives estimates of droplet cooling effectiveness that agree well with results from the numerical model. The analytical model predicts that for fixed Reynolds number ( Re ) cooling effectiveness increases with Weber number ( We ). However, for large Weber numbers, when We ≫ Re 0.5 , cooling effectiveness is independent of droplet velocity or size and depends only on the Prandtl number.

The Effect of Dissolving Gases or Solids in Water Droplets Boiling on a Hot Surface

We conducted experiments on the effect of dissolving either a gas (carbon dioxide) or a solid salt (sodium carbonate or sodium bicarbonate) in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 100°C to 300°C. We recorded the boiling of droplets with a video system, and photographed droplet impact using short-duration flash photography. At surface temperatures that were too low to initiate nucleate boiling, dissolved salts were found to reduce the evaporation rate since they lower the vapor pressure of water. Dissolved gas had the opposite effect: it came out of solution and formed bubbles in the liquid, enhancing evaporation. In the nucleate boiling regime dissolved carbon dioxide enhanced heat transfer by a small amount. However, sodium carbonate prevented coalescence of vapor bubbles and produced foaming in the droplet, greatly enhancing heat transfer and reducing the droplet lifetime to approximately half that of a pure water drop. Sodium bicarbonate, which decomposes to give carbon dioxide and sodium carbonate when heated, produced an even larger enhancement of heat transfer. When the surface temperature was raised above the Leidenfrost temperature of water, droplets went into film boiling and bounced off the surface following impact. Dissolved carbon dioxide was found to suppress heterogeneous bubble formation in the droplet during impact. However, dissolved salts promoted bubble formation and led to droplet break-up during impact.

Experiments on adding a surfactant to water drops boiling on a hot surface

The effect of adding a surfactant (sodium dodecyl sulphate) to droplets boiling on a hot stainless steel surface was studied. Experiments were done using solutions containing 100 ppm and 1000 ppm by weight of surfactant and the results compared with those for droplets of pure water. Surface temperature was varied from 60 to 340 degrees C. Droplet impact and evaporation was photographed using both video and 35 mm cameras. Addition of the surfactant significantly reduced lifetimes of droplets in a state of evaporation or nucleate boiling. For surface temperatures below those required to initiate nucleate boiling, the principal effect of the surfactant was to reduce liquid–solid contact angle, increasing the surface area wetted by the drop. At higher surface temperatures, the surfactant promoted vapour bubble nucleation and foaming in the liquid, greatly enhancing heat transfer. Increasing surfactant concentration reduced the Leidenfrost temperature, above which droplets were levitated above the surface on a thin film of their own vapour. The surfactant had no effect on evaporation time of droplets in film boiling.

Boiling of droplets on a hot surface in low gravity

The boiling of single droplets of water and n-heptane on a hot stainless steel surface was observed in a low gravity environment, obtained on board a platform in free fall. Droplet impact was photographed using a single-shot flash-photographic method. Surface temperature variation during droplet impact was recorded using a fast-response thermocouple. Droplets could not be maintained in stable film boiling in low gravity: the pressure of vapour under droplets pushed them away from the surface. Nucleate boiling of droplets was not affected by a reduction in gravity. Vapour bubbles nucleating on the solid surface separated and rose into the liquid even in the absence of buoyancy forces.

IMPACT OF N-HEPTANE DROPLETS ON A HOT SURFACE IN LOW GRAVITY

Experiments were done to observe droplets of n-heptane impacting on a hot stainless steel surface in a low gravity environment. Impacting droplets were photographed using a single-shot flash-photographic method. Cellular structures were observed in the spreading liquid film, even in absence of buoyancy forces, when surface temperatures exceeded 80°C. The cells were attributed to surface tension driven flows in the liquid. A simple heat conduction model was used to estimate temperature gradients in the liquid film, and to calculate the Marangoni Number (Ma). The onset of cellular structures in the liquid film corresponded to Ma&gt;80, confirming predictions from instability theory. Droplets in Leidenfrost evaporation were pushed away from the surface by the pressure of the vapour below them. Reducing gravity level had no influence on the dynamics of droplet impact, or on bubble movement in nucleate boiling.

Effect of Coating Thickness on the Vaporization of a Liquid Droplet on a Hot Surface Coated with Flame-Sprayed Ceramics.

Vaporization phenomena of a single liquid droplet on a hot stainless steel surface coated with flame-sprayed zirconia were investigated experimentally. Coating thickness of the test surface was in the range from 0.18 to 0.92 mm. Lifetime curves for several pure liquid drops were measured at surface temperatures up to 1100 K, and time-averaged heat flux transferred from the surface to the drop during its lifetime was analyzed. The results show that the extent of the wide temperature range within which the drop remained in direct contact with the surface and vaporized quickly was kept almost constant for thicknesses of more than about 0.3 mm owing to low thermal conductivity of the coating layer. The quantity of heat transferred from the surface during a given period of time, calculated from one-dimensional analysis, also showed a similar dependency on the coating thickness.